1. Field of the Invention
The present invention relates generally to semiconductor integrated circuits, and more specifically to formation of a contact structure for such circuits.
2. Description of the Prior Art
In fabricating semiconductor integrated circuits, the integrity of various structures on the circuit is of great importance. Undesirable impurities in the wrong portions of a circuit can adversely affect its functioning.
One type of structure commonly found on a semiconductor integrated circuit is a contact from an upper level metal interconnect layer to a lower conductive structure through a contact via. An interlevel dielectric through which the contact via is cut often has a reflow glass layer to improve planarity of the chip's surface. This glass layer typically has impurities which can migrate into the metal interconnect in the via and adversely affect its operation. For example, it is known that mobile ion donation from glass layers in contact with metal interconnect can shift data retention voltages in memory circuits. Also, outgassing of solvents in such a glass layer can cause voiding in, or oxidation of, sputtered metal interconnect.
Since the formation of a reflowable glass layer improves the planarity of the integrated circuit, it is important to use such material in interlevel dielectric layers. It would be desirable to provide a technique which allows the planarity improvement of a reflowable glass without contamination of interconnect by the impurities used in standard glasses.